The present invention relates to a method for measuring a flow rate and a flow velocity of a fluid by utilizing ultrasonic wave, and an ultrasonic flow rate meter. And, it also relates to a method for measuring a temperature or pressure of a fluid without contact by utilizing ultrasonic wave, and an ultrasonic thermometer and an ultrasonic pressure gage.
Recently, for a flow rate meter for measuring a flow rate of a fluid, an ultrasonic flow rate meter which utilizes ultrasonic wave has been used.
In the ultrasonic flow rate meter, oscillators are disposed in a conduit for flowing the fluid at a longitudinal direction spaced. And, an ultrasonic wave is emitted from the one oscillator and received by the other oscillator, while an ultrasonic wave are emitted from the other oscillator and received by the one oscillator. By a difference in a nultrasonic wave propagation time from the emission to the reception in each case, a flow velocity of the fluid in the conduit is obtained, whereby a flow rate thereof will be determined.
And, for a thermometer or a pressure gage for measuring a temperature or a pressure of a fluid, an ultrasonic thermometer or an ultrasonic pressure gage, which utilize a semiconductor sensor, has been proposed.
Such the conventional ultrasonic flow rate meter employs the time difference method or the phase difference method, as measurement method. The ultrasonic wave propagation time varies according to a property, a temperature and a pressure condition of the propagation material. If a flow rate is so large that a variation range in the propagation time can be neglected as an error, there will be no problem. However, when the flow rate is too small for the variation range, it will be difficult to determine the flow rate accurately due to such the variations.
And, it is difficult to arrange such the conventional thermometer or the pressure gage at a same place where a flow velocity is measured by an ultrasonic flow meter. Also, it is difficult to measure a temperature or a pressure of a fluid without contact to the fluid without preventing the fluid flow.
In view of the problems, the object of the present invention is to provide a flow rate measurement method and a flow velocity measurement method by utilizing an improved measurement method (a frequency variable method) by which a flow rate can be measured accurately, and an ultrasonic flow rate meter. In the method, because a phase of the received ultrasonic wave varies in response to a flow velocity V in the conduit, a frequency of the transmitted ultrasonic wave will be changed by a PLL circuit such that the phase becomes equal to a phase under a condition of a flow velocity in the conduit being zero (V=0). Here, since the changed frequency relates a flow velocity, measuring the difference in the frequency will determine the flow velocity accurately.
Further, the object of the present invention is to provide, a temperature and a pressure measurement methods by utilizing an improved measurement method (a frequency variable method) by which a temperature or a pressure can be measured accurately, an ultrasonic thermometer and an ultrasonic pressure gage. In the method, because a phase of the received ultrasonic wave varies in response to a time difference of an ultrasonic velocity in the conduit, the time difference being caused by a change in a temperature or a pressure of the fluid in the conduit, a frequency of the transmitted ultrasonic wave will be changed by a PLL circuit such that the phase becomes equal to a phase under a condition of a reference temperature (for example, 20xc2x0 C.) in the conduit. Since the changed frequency relates a temperature and a pressure in the conduit, measuring the difference in the frequency will be determine the temperature or the pressure of the fluid in the conduit accurately.
In order to solve the problems, the present invention provides a flow rate measurement method, which measures a flow rate of a fluid flowing through a conduit, comprises the following steps: preparing a reference ultrasonic velocity such that the fluid is in a standard condition, measuring an ultrasonic velocity A by transmitting an ultrasonic wave from one side and receiving the ultrasonic wave at the other side in the fluid flowing through the conduit, measuring an ultrasonic velocity B by transmitting an ultrasonic wave from the other side and receiving the ultrasonic wave at the one side in the fluid flowing through the conduit, averaging the ultrasonic velocity A and the ultrasonic velocity B thereby to obtain an absolute ultrasonic velocity in the fluid, dividing a difference between the ultrasonic velocity A and the ultrasonic velocity B by 2 thereby to obtain a temporary flow velocity of the fluid, correcting the temporary flow velocity by using a difference between the reference ultrasonic velocity and the absolute ultrasonic velocity thereby to determine an accurate flow velocity of the fluid, and determining a flow rate of the fluid by using the accurate flow velocity and a cross section area of the conduit.
In the flow rate measurement method according to the present invention, the ultrasonic velocities A and B, variable by a temperature or a pressure of the fluid flowing through the conduit, are obtained by a transmission and a reception of an ultrasonic wave. So, an accurate flow velocity can be determined by correcting the temporary flow velocity without measurement of a temperature or a pressure of the fluid. Accordingly, a flow rate of the fluid can be determined accurately.
The ultrasonic flow rate meter according to the present invention, which measures a flow rate of a fluid flowing through a conduit, comprises the following devices: a first ultrasonic wave transmission and reception device disposed on the outside of the conduit, a second ultrasonic wave transmission and reception device disposed on the outside of the conduit part away from the first ultrasonic wave transmission and reception device, a first phase difference detector connected to the second ultrasonic wave transmission and reception device, a first PLL type loop connection disposed between the first phase difference detector and the first ultrasonic wave transmission and reception device, a second phase difference detector connected to the first ultrasonic wave transmission and reception device, a second PLL type loop connection disposed between the second phase difference detector and the second ultrasonic wave transmission and reception device, and a measurement controller for obtaining a flow rate of the fluid.
The ultrasonic flow rate meter according to the present invention is provided with a measurement controller, which measures, controls and operates in a manner described as follows. In a fluid flowing through a conduit at a flow velocity Vx, an ultrasonic wave transmitted from the first ultrasonic wave transmission and reception device is received by the second ultrasonic wave transmission and reception device. Then, a phase difference in the ultrasonic wave at the transmission and the reception will be detected by the first phase difference detector.
When the phase difference is detected, a transmission frequency of the first ultrasonic wave transmission and reception device is gradually changed by the first loop connection until the phase difference becomes zero, and thus a transmission frequency is determined when the phase difference becomes zero. From the determined transmission frequency or the wavelength, an ultrasonic velocity A in the fluid will be obtained.
Next, an ultrasonic wave transmitted from the second ultrasonic wave transmission and reception device is received by the first ultrasonic wave transmission and reception device. Then, a phase difference in the ultrasonic wave at the transmission and the reception is detected by the second phase difference detector.
When the phase difference will be detected, a transmission frequency of the second ultrasonic wave transmission and reception device is gradually changed by the second loop connection until the phase difference becomes zero, and thus a transmission frequency is determined when the phase difference becomes zero. From the determined transmission frequency or the wavelength, an ultrasonic velocity B in the fluid will be obtained.
Then, an average of the ultrasonic velocity A and the ultrasonic velocity B is calculated in order to obtain an absolute ultrasonic velocity in the fluid. Next, a difference between the ultrasonic velocity A and the ultrasonic velocity B is divided by 2 in order to determine a temporary flow velocity of the fluid. Next, a reference ultrasonic velocity is prepared such that the fluid is in a standard condition. Then, by using a difference between the reference ultrasonic velocity and the absolute ultrasonic velocity, the temporary flow velocity will be corrected, whereby an accurate flow velocity Vx of the fluid is obtained.
Then, the obtained flow velocity Vx and a cross section area of the conduit can determine a flow rate of the fluid. Accordingly, the accurate flow velocity of the fluid can be obtained by utilizing such a frequency that the phase difference in an ultrasonic wave becomes zero, without measurement of a temperature or a pressure of the fluid.
In the ultrasonic flow rate meter according to the present invention, the first ultrasonic wave transmission and reception device may be constructed of a first ultrasonic wave transmitter and a first ultrasonic wave receiver, and the second ultrasonic wave transmission and reception device may be constructed of a second ultrasonic wave transmitter and a second ultrasonic wave receiver. And, the first phase difference detector and the second phase difference detector may be combined to be a phase difference detector. Also, the first loop connection and the second loop connection may be combined to be a loop connection.
The ultrasonic flow rate meter according to the present invention, which measures a flow rate of a fluid flowing through a conduit, comprises the following devices: an ultrasonic wave transmitter disposed in the conduit, an ultrasonic wave receiver disposed at a predetermined distance from the ultrasonic wave transmitter, a PLL circuit connected to the ultrasonic wave transmitter and the ultrasonic wave receiver, and a measurement controller for obtaining an oscillating frequency of an oscillator and converting the oscillating frequency to a flow rate. The PLL circuit has a phase difference detector for detecting a phase difference between an ultrasonic wave transmitted from the ultrasonic wave transmitter and an ultrasonic wave received by the ultrasonic wave receiver, an integrating circuit for integrating an output waveform outputted from the phase difference detector, and said oscillator, which is controlled by an output signal outputted from the integrating circuit.
Further, an ultrasonic flow rate meter according to the present invention may comprise two sets of the ultrasonic flow rate meter.
The ultrasonic flow rate meter according to the present invention, which measures a flow rate of a fluid flowing through a conduit, comprises the following devices: an ultrasonic wave transmitter disposed in the conduit, a first ultrasonic wave receiver and a second ultrasonic wave receiver disposed at a predetermined distance from the ultrasonic wave transmitter in the opposite direction respectively, a PLL circuit connected to the ultrasonic wave transmitter, a switching device connected to the PLL circuit, and a measurement controller for obtaining an oscillating frequency of an oscillator and converting the oscillating frequency to a flow rate. The switching device alternatively changes connection of the PLL circuit to be connected either to the first ultrasonic wave receiver or to the second ultrasonic wave receiver. And, the PLL circuit has a phase differences detector for detecting a phase difference between an ultrasonic wave transmitted from the ultrasonic wave transmitter and an ultrasonic wave received by the first or the second ultrasonic wave receiver respectively, an integrating circuit for integrating an output waveform outputted from the phase difference detector, and said oscillator, which is controlled by an output signal outputted from the integrating circuit.
The ultrasonic flow rate meter according to the present invention, which measures a flow rate of a fluid flowing through a conduit, comprises the following devices: an ultrasonic wave generator for generating an ultrasonic wave, an ultrasonic wave transmitter disposed in the conduit, the transmitter transmitting an ultrasonic wave generated from the ultrasonic wave generator, an ultrasonic wave receiver disposed at a predetermined distance from the ultrasonic wave transmitter, a phase difference detector for detecting a phase difference between an ultrasonic wave transmitted from the ultrasonic wave transmitter and an ultrasonic wave received by the ultrasonic wave receiver, an integrating circuit for integrating an output waveform outputted from the phase difference detector, an oscillator controlled by an output signal outputted from the integrating circuit, and a measurement controller for obtaining an oscillating frequency of the oscillator and converting the oscillating frequency to a flow rate.
The ultrasonic flow rate meter according to the present invention, which measures a flow rate of a fluid flowing through the conduit, comprises the following devices: a first ultrasonic wave transmission and reception device disposed in the conduit, a second ultrasonic wave transmission and reception device disposed at a predetermined distance from the first ultrasonic wave transmission and reception device, a switching device connected to the first and second ultrasonic wave transmission and reception devices, a PLL circuit connected to the switching device, and a measurement controller for obtaining an oscillating frequency of an oscillator and converting the oscillating frequency to a flow rate. The switching device alternatively changes connection of the PLL circuit such that the input thereof is connected to the first ultrasonic wave transmission and reception device and also the output thereof is connected to the second ultrasonic wave transmission reception device, or such that the input thereof is connected to the second ultrasonic wave transmission and reception device and also the output thereof is connected to the first ultrasonic wave transmission and reception device. And, the PLL circuit has a phase difference detector for detecting a phase difference between an ultrasonic wave transmitted from the first or the second ultrasonic wave transmission and reception device and an ultrasonic wave received by the second or the first ultrasonic wave transmission and reception device, an integrating circuit for integrating an output waveform outputted from the phase difference detector and an oscillator controlled by an output signal outputted from the integrating circuit.
The ultrasonic flow rate meter according to the present invention, which measures a flow rate of a fluid flowing through a conduit, comprises the following devices: an ultrasonic wave generator for generating an ultrasonic wave, a first ultrasonic wave transmission and reception device disposed in the conduit, a second ultrasonic wave transmission and reception device disposed in the conduit at a predetermined distance from the first ultrasonic wave transmission and reception device, the devices transmitting and receiving an ultrasonic wave generated from the ultrasonic generator, a switching device connected to the first and second ultrasonic wave transmission and reception devices, a phase difference detector connected to the switching device, the detector detecting a phase difference between an ultrasonic wave transmitted from the first or the second ultrasonic wave transmission and reception device and an ultrasonic wave received by the second or the first ultrasonic wave transmission and reception device respectively, an integrating circuit for integrating an output waveform outputted from the phase difference detector, an oscillator controlled by an output signal outputted from the integrating circuit, and a measurement controller for obtaining an oscillating frequency of the oscillator and converting the oscillating frequency to a flow rate. The switching device alternatively changes connection of the input of the phase difference detector to be connected either to the first ultrasonic wave transmission and reception device, or to the second ultrasonic wave transmission and reception device.
A flow velocity measurement method according to the present invention, which measures a flow velocity of a fluid flowing through a conduit, comprises the following steps: preparing a reference ultrasonic velocity such that the fluid is in a standard condition, measuring an ultrasonic velocity A by transmitting an ultrasonic wave from one side and receiving the ultrasonic wave at the other side in the fluid flowing through the conduit, measuring an ultrasonic velocity B by transmitting an ultrasonic wave from the other side and receiving the ultrasonic wave at the one side in the fluid flowing through the conduit, averaging the ultrasonic velocity A and the ultrasonic velocity B thereby to obtain an absolute ultrasonic velocity in the fluid, dividing a difference between the ultrasonic velocity A and the ultrasonic velocity B by 2 thereby to obtain a temporary flow velocity of the fluid, and correcting the temporary flow velocity by using a difference between the reference ultrasonic velocity and the absolute ultrasonic velocity thereby to determine an accurate flow velocity of the fluid.
A measurement method according to the present invention, which measures a temperature or a pressure of a fluid flowing through a conduit, comprises the following steps: preparing a reference ultrasonic velocity such that the fluid is in a standard condition (for example, at 20xc2x0 C.), measuring an ultrasonic velocity A by transmitting an ultrasonic wave from one side and receiving the ultrasonic wave at the other side in the fluid flowing through the conduit, measuring an ultrasonic velocity B by transmitting an ultrasonic wave from the other side and receiving the ultrasonic wave at the one side in the fluid flowing through the conduit, averaging the ultrasonic velocity A and the ultrasonic velocity B thereby to obtain an absolute ultrasonic velocity in the fluid, dividing a difference between the ultrasonic velocity A and the ultrasonic velocity B by 2 thereby to obtain a temporary flow velocity of the fluid, correcting the temporary flow velocity by using a difference between the reference ultrasonic velocity and the absolute ultrasonic velocity thereby to determine an accurate flow velocity of the fluid, and multiplying the accurate flow velocity by a cross section area of the conduit thereby to obtain a flow rate, at the same time obtaining a relationship between a temperature and a pressure by the reference ultrasonic velocity and the absolute ultrasonic velocity, and finally obtaining a pressure or a temperature of the fluid by the relationship and a predetermined temperature or a predetermined pressure of the fluid.
In the measurement method for measuring a temperature or a pressure, since the ultrasonic velocities A and B, variable by a temperature and a pressure of the fluid flowing through the conduit, are measured by using a transmission and a reception of an ultrasonic wave, a flow velocity of the fluid can be measured accurately by correction of the temporary flow velocity only, without measurement of a temperature or a pressure of the fluid. At the same time, a relationship between a temperature and a pressure, which is previously provided by the reference ultrasonic velocity and the absolute ultrasonic velocity, and a predetermined temperature or a predetermined pressure of the fluid can determine a pressure and a temperature of the fluid.
Here, the ultrasonic velocity (the absolute ultrasonic velocity) is shown as a function of a flow velocity, a temperature and a pressure of the fluid. Therefore, a measurement of the absolute ultrasonic velocity and the flow velocity can determine a pressure of the fluid as long as a temperature of the fluid is previously known, and a temperature of the fluid as long as a pressure of the fluid is previously known. Accordingly, a flow velocity and a temperature or a pressure can be measured at the same time.
A measurement method according to the present invention, which measures a temperature or a pressure of a fluid flowing through a conduit, comprises the following steps: preparing a reference ultrasonic velocity such that the fluid is in a standard condition (for example, at 20xc2x0 C.), measuring ultrasonic velocity A by transmitting an ultrasonic wave from one side and receiving the ultrasonic wave at the other side in the fluid flowing through the conduit, measuring ultrasonic velocity B by transmitting an ultrasonic wave from the other side and receiving the ultrasonic wave at the one side in the fluid flowing through the conduit, averaging the ultrasonic velocity A and the ultrasonic velocity B thereby to obtain an absolute ultrasonic velocity in the fluid, obtaining a relationship between a temperature and a pressure by a difference between the reference ultrasonic velocity and the absolute ultrasonic velocity, and obtaining a pressure or a temperature of the fluid by the relationship and a predetermined temperature or a predetermined pressure of the fluid.
In the measurement method for measuring a temperature or a pressure according to the present invention, a relationship between the reference ultrasonic velocity and the absolute ultrasonic velocity is obtained. And, such the relationship and a predetermined temperature or a predetermined pressure of the fluid can determine a pressure and a temperature of the fluid without contact to the fluid.
Here, the ultrasonic velocity (the absolute ultrasonic velocity) is shown as a function of a flow velocity, a temperature and a pressure of the fluid. Therefore, a measurement of the absolute ultrasonic velocity and the flow velocity can determine a pressure of the fluid as long as a temperature of the fluid is previously known, and a temperature of the fluid as long as a pressure of the fluid is previously known.
An ultrasonic thermometer or an ultrasonic pressure gage according to the present invention, which measures a temperature or a pressure of a fluid flowing through a conduit, comprises the following devices: a first ultrasonic wave transmission and reception device disposed on the outside of the conduit, a second ultrasonic wave transmission and reception device disposed on the outside of the conduit, the second device being spaced from the first ultrasonic wave transmission and reception device, a first phase difference detector connected to the second ultrasonic wave transmission and reception device, a first PLL type loop connection disposed between the first phase difference detector and the first ultrasonic wave transmission and reception device, a second phase difference detector connected to the first ultrasonic wave transmission and reception device, a second PLL type loop connection disposed between the second phase difference detector and the second ultrasonic wave transmission and reception device, and a measurement controller for obtaining a temperature or pressure of the fluid.
The ultrasonic thermometer or the ultrasonic pressure gage according to the present invention is provided with a measurement controller, which measures, controls and operates in a manner described as follows. In the fluid flowing through the conduit at the flow velocity Vx, an ultrasonic wave transmitted from the first ultrasonic wave transmission and reception device is received by the second ultrasonic wave transmission and reception device. Then, a phase difference in the ultrasonic wave at the transmission and the reception will be detected by the first phase difference detector.
When the phase difference is detected, a transmission frequency of the first ultrasonic wave transmission and reception device is gradually changed by the first loop connection until the phase difference becomes zero, and thus a transmission frequency is determined when the phase difference becomes zero. From the determined transmission frequency or the wavelength, an ultrasonic velocity A in the fluid will be obtained.
Next, an ultrasonic wave transmitted from the second ultrasonic wave transmission and reception device is received by the first ultrasonic wave transmission and reception device. Then, a phase difference in the ultrasonic wave at the transmission and the reception is detected by the second phase difference detector.
When a phase difference will be detected, a transmission frequency of the second ultrasonic wave transmission and reception device is gradually changed by the second loop connection until the phase difference becomes zero, and thus the transmission frequency is determined when the phase difference becomes zero. From the determined transmission frequency or the wavelength, an ultrasonic velocity B in the fluid will be obtained.
Next, an average of the ultrasonic velocity A and the ultrasonic velocity B is calculated in order to obtain an absolute ultrasonic velocity in the fluid. Then, a difference between the ultrasonic velocity A and the ultrasonic velocity B is divided by 2 in order to determine a temporary flow velocity of the fluid. Next, a reference ultrasonic velocity such that the fluid is in a standard condition (for example, at 20xc2x0 C.). And, a relationship between a temperature and a pressure, which is previously provided by the reference ultrasonic velocity and the absolute ultrasonic velocity, and a predetermined temperature or a predetermined pressure of the fluid can determine a pressure or a temperature of the fluid.
In the ultrasonic thermometer or the ultrasonic pressure gage according to the present invention, the first ultrasonic wave transmission and reception device may be constructed of a first ultrasonic wave transmitter and a first ultrasonic wave receiver, and the second ultrasonic wave transmission and reception device may be constructed of a second ultrasonic wave transmitter and a second ultrasonic wave. And, the first phase difference detector and the second phase difference detector may be combined to be a phase difference detector. Also, the first loop connection and the second loop connection may be combined to be a loop connection.
An ultrasonic thermometer or an ultrasonic pressure gage according to the present invention, which measures a temperature or a pressure of a fluid flowing through a conduit, comprises the following devices: an ultrasonic wave transmitter disposed in the conduit, an ultrasonic wave receiver disposed at a predetermined distance from the ultrasonic wave transmitter, a PLL circuit connected to the ultrasonic wave transmitter and the ultrasonic wave receiver, and a measurement controller for controlling to obtain an oscillating frequency of an oscillator and converting the oscillating frequency to a flow rate. The PLL circuit has a phase difference detector for detecting a phase difference between an ultrasonic wave transmitted from the ultrasonic wave transmitter and an ultrasonic wave received by the ultrasonic wave receiver, an integrating circuit for integrating an output waveform outputted from the phase difference detector, and said oscillator, which is controlled by an output signal outputted from the integrating circuit.
An ultrasonic thermometer or an ultrasonic pressure gage according to the present invention, which measures a temperature or a pressure of a fluid flowing through a conduit, comprises the following devices: an ultrasonic wave transmitter disposed in the conduit, a first ultrasonic wave receiver and a second ultrasonic wave receiver disposed at a predetermined distances from the ultrasonic wave transmitter in the opposite directions, a PLL circuit connected to the ultrasonic wave transmitter, a switching device connected to the PLL circuit, and a measurement controller for obtaining an oscillating frequency of an oscillator and converting the oscillating frequency to a flow rate. The switching device alternatively changes connection of the PLL circuit to be connected either to the first ultrasonic wave receiver or to the second ultrasonic wave receiver respectively. The PLL circuit has a phase differences detector for detecting a phase difference between an ultrasonic wave transmitted from the ultrasonic wave transmitter and an ultrasonic wave received by the first and second ultrasonic wave receivers, an integrating circuit for integrating an output waveform outputted from the phase difference detector and said oscillator, which is controlled by an output signal outputted from the integrating circuit.
An ultrasonic thermometer or an ultrasonic pressure gage according to the present invention, which measures a temperature or a pressure of a fluid flowing through a conduit, comprises the following devices: an ultrasonic wave generator for generating an ultrasonic wave, an ultrasonic wave transmitter disposed in the conduit, the transmitter transmitting an ultrasonic wave generated from the ultrasonic wave generator, an ultrasonic wave receiver dispose data predetermined distance from the ultrasonic wave transmitter, a phase difference detector for detecting a phase difference between an ultrasonic wave transmitted from the ultrasonic wave transmitter and an ultrasonic wave received by the ultrasonic wave receiver, an integrating circuit for integrating an output waveform outputted from the phase difference detector, an oscillator controlled by an output signal outputted from the integrating circuit, and a measurement controller for obtaining an oscillating frequency of the oscillator and converting the oscillating frequency to a temperature or pressure.
An ultrasonic thermometer or an ultrasonic pressure gage according to the present invention, which measures a temperature or a pressure of a fluid flowing through a conduit, comprises the following devices: a first ultrasonic wave transmission and reception device disposed in the conduit, a second ultrasonic wave transmission and reception device disposed at a predetermined distance from the first ultrasonic wave transmission and reception device, a switching device connected to the first and second ultrasonic wave transmission and reception devices, a PLL circuit connected to the switching device, and a measurement controller for obtaining an oscillating frequency of an oscillator and converting the oscillating frequency to a temperature or a pressure. The switching device alternatively changes connection of the PLL circuit such that the input thereof is connected to the first ultrasonic wave transmission and reception device and also the output thereof is connected to the second ultrasonic wave transmission and reception device, or such that the input thereof is connected to the second ultrasonic wave transmission and reception device and also the output thereof is connected to the first ultrasonic wave transmission and reception device. And, the PLL circuit has a phase difference detector for detecting a phase difference between an ultrasonic wave transmitted from the first or the second ultrasonic wave transmission and reception device and an ultrasonic wave received by the second or the first ultrasonic wave transmission and reception device, an integrating circuit for integrating an output waveform outputted from the phase difference detector, and an oscillator controlled by an output signal outputted from the integrating circuit.
An ultrasonic thermometer or an pressure gage according to the present invention, which measures a temperature or a pressure of a fluid flowing through a conduit, comprises the following devices: an ultrasonic wave generator for generating ultrasonic wave, a first ultrasonic wave transmission and reception device disposed in the conduit, a second ultrasonic wave transmission and reception device disposed in the conduit at a predetermined distance from the first ultrasonic wave transmission and reception device, the devices transmitting and receiving an ultrasonic wave generated from the ultrasonic generator, a switching device connected to the first and second ultrasonic wave transmission and reception devices, a phase difference detector connected to the switching device, the detector detecting a phase difference between an ultrasonic wave transmitted from the first or the second ultrasonic wave transmission and reception device and an ultrasonic wave received by the second or the first ultrasonic wave transmission and reception device, an integrating circuit for integrating an output wave form outputted from the phase difference detector, an oscillator controlled by an output signal outputted from the integrating circuit, and a measurement controller for obtaining an oscillating frequency of the oscillator and converting the oscillating frequency to a temperature or a pressure. The switching device alternatively changes connection of the input of the phase difference detector to be connected either to the first ultrasonic wave transmission and reception device, or to the second ultrasonic wave transmission and reception device.